Speaker drivers convert an electrical signal to sound by inducing a current in a voice coil that is within a permanent magnetic field. The magnetic field produced by the voice coil current interacts with the permanent magnet field and causes movement of the voice coil. The voice coil is wound around a voice coil former and is attached to a cone which causes air movement and sound to propagate. A basket provides a frame to support the large diameter of the cone through a flexible surround. The former attached at the small end of the cone is stabilized by a spider, which allows movement along the axis of the cone and voice coil and restrains lateral motion.
Drivers are produced in a range of sizes. The smallest, a tweeter, is used for reproducing the high frequency end of the audio range. A midrange driver is used for reproducing the mid range of the audio spectrum. A woofer driver is used for the lower end of the audio spectrum. At the extreme low end of the audible range, and below, a sub-woofer driver is used. At lower audio frequencies more air volume needs to be moved. This requires a larger cone and a higher displacement in the motion of the cone. In order to move a large volume of air with a speaker driver mounted in a small enclosure, a large permanent magnet is needed and a high voice coil current.
The permanent magnet, T-yoke, and gap plate are referred to as the motor. In a conventional speaker driver, the motor is attached to the basket using screws that are inserted from inside the basket, underneath the cone, passing through holes in the basket and threading into the gap plate. Once the surround is attached to the basket, the removal of the motor is prevented because the attachment screws are no longer accessible. This arrangement dictates a specific sequence in manufacturing, where the motor must be attached to the basket prior to the voice coil, cone, and surround being assembled.
U.S. Pat. No. 4,234,766 “speaker assembly” issued to Cacho describes a speaker assembly with a detachable cone unit that may be removed from a base and replaced with a larger or smaller capacity speaker. This disclosure is directed to a small speaker and does not address the problem of removing the motor portion of the speaker driver from the basket after assembly. The detachable cone unit is a complete speaker driver including a cone, coil, and magnet.
Large drivers present manufacturing, shipping, and installation difficulties due to the heavy product. The cost is higher due to the large components. A substantial portion of the weight of the driver is represented by the motor. When damage occurs to the surround, cone, voice coil, or spider the driver must be shipped to a repair facility for replacement of the damaged parts.